Matthias Schabel wrote:
The problem domain is fluid dynamics so enter the Kv and Cv values.
Technically these are a measure of volumetric flow. For instance, Kv is defined as:
the flow of water with temperature ranging 5 - 30 oC through a valve in cubic meters per hour (m3/h) with a pressure drop of 1 bar
The problem is that engineers see this as a "unitless" value and treat it as having no units at all. They use Kv in SI based equations, not m3/s as we'd expect. Thus all equations being fed to us use Kv as if it were a natural part of the equation.
Most of the time these dimensions do not compute dimensionally anyway but there's rare cases when they do. I have gotten the engineers (those giving me specs for code I write) to decide on Kv instead of doing both Kv and Cv (it's a basic conversion).
It's a little hard to see where the problem is without a concrete example. How about one equation and the corresponding function, with ancillary information about the expected units of inputs/output?
I'll try, but I'm not an engineer. I believe the "flow coefficient" (Kv) is mostly used in calculating flow through valves and fittings. It has a relationship with a "resistance coefficient" (K) in that: K = C1 * pi^2 * d^4 / Kv^2 Kv = C2 * pi * d^2 / K^.5 d is the valve diameter. C1 and C2 are really large numbers. The volumetric flow (Q) can then be found: Q = C * Kv * ( dP / p )^.5 Where C is a constant, dP is a pressure, and p is a density. That equation might look a bit different for SI (that's in some set of US units, not necessarily a true system) but the point is that Kv will still be in cubic meters per hour. TP410 states, "At the time of preparation of this paper there is no agreed international definition for flow coefficient in the terms of SI units." That was 50 years ago or something and it's not changed. It should be possible to convert Kv into m3/s but the equations the engineers work in, and thus will be giving me and are in our sources, simply do not use this unit for that variable even if everything else is in SI.